Rank G H, Xiao W, Arndt G M
Department of Biology, University of Saskatchewan, Saskatoon, Canada.
Genome. 1994 Feb;37(1):12-8. doi: 10.1139/g94-002.
The 2-microns plasmid of industrial and laboratory strains of Saccharomyces cerevisiae exists as two main polymorphic forms designated type I and type II. Polymorphism is restricted to the 3200-bp right unique region where types I and II show approximately 10% nucleotide divergence in trans-acting REP1 and RAF loci and 30% divergence in the cis-acting STB locus. In addition, the cis-acting STB plasmid partition locus of type II plasmids varies in sequence and copy number of a 125-bp repeat. We devised chimeric and 2-microns plasmid stability experiments to evaluate the effect of STB polymorphism on plasmid fitness in amphiploid industrial and haploid laboratory strains. Reciprocal experiments of type-II STB chimeric plasmids in type-I bakers' yeast or a type-I chimeric plasmid in type-II distillers', wine, or haploid strains showed similar partition efficiencies. However, chimeric and 2-microns plasmids carrying a 250-bp STB from a type-II haploid strain had reduced fitness in a type-II industrial wine strain. These results in conjunction with molecular analyses of 2-microns-like and 2-microns plasmids indicates the coevolution of STB with trans-acting plasmid and host-cell factors.
酿酒酵母工业菌株和实验室菌株的2微米质粒以两种主要的多态形式存在，分别称为I型和II型。多态性仅限于3200 bp的右侧独特区域，其中I型和II型在反式作用的REP1和RAF位点显示约10%的核苷酸差异，在顺式作用的STB位点显示30%的差异。此外，II型质粒的顺式作用STB质粒分配位点在125 bp重复序列的序列和拷贝数上有所不同。我们设计了嵌合和2微米质粒稳定性实验，以评估STB多态性对双倍体工业菌株和单倍体实验室菌株中质粒适应性的影响。在I型面包酵母中对II型STB嵌合质粒进行的互作实验，或在II型酿酒酵母、葡萄酒酵母或单倍体菌株中对I型嵌合质粒进行的互作实验，显示出相似的分配效率。然而，携带来自II型单倍体菌株的250 bp STB的嵌合质粒和2微米质粒在II型工业葡萄酒酵母菌株中的适应性降低。这些结果与对2微米样质粒和2微米质粒的分子分析相结合，表明STB与反式作用质粒和宿主细胞因子共同进化。
